It often occurs that during device manufacture in fab at most of process steps (i.e., Litho, handling, etching, deposition, layers growth, metallization and others) defects are created as a result of machine malfunction and/or process flow instability caused by chemicals or other delivered materials participating the process.
The presence of defects may impair the quality of the final product. The yield and productivity are adversely affected if the defect presence is not detected in time. Therefore, inspecting wafers for defects is widely implemented in semiconductor manufacturing processes and procedures.
When defects are detected in time, it may be possible to take appropriate remedial action, such as defected wafer re-processing, or defective wafer exclusion from consequent process flow. Close monitoring and awareness of the operational quality of the processing tool and its maintenance initiation are attained as well.
Prior art methods are known that perform surface inspection by contrast variation analysis during the manufacturing process. In contrast thereto, the method according to the invention may also be implemented off-process, i.e., using a standalone inspection tool may or may not be integrated with the host system. Furthermore, unlike known inspection tools, the invention performs instantaneous imaging and illumination of the entire wafer.
There is still further need for a method and apparatus capable of fast execution of the imaging and computation tasks of the defects detection processes during fabrication, to permit incorporation of inspection processes in the host tool production cycle timeframe. Integration of the inspection tool in the host system requires instantaneous or almost instantaneous image acquisition of the wafer surface under test, and accordingly illumination of the complete wafer sample, while accommodating the constraints of the parent tool space, operation dynamics and cycle. Moreover, tailored, task-oriented defects detection and optimized image processing manipulation algorithms are needed. Furthermore, there is a need for metrology quantification and characterization of detected defects and appropriate database accumulation for consequent process tool integrity evaluation and preventive maintenance prompting.
WO 2006/046236 in the name of the present applicant discloses an automatic optical inspection apparatus and method for residue detection on polished wafers, including an illumination source capable of instantaneous entire wafer surface illumination, a color digital camera, encompassing the entire wafers surface without eclipse, in a duple of consecutive, properly delayed imaging shots and provides appropriate image resolution for tiny residue detection, computation means, implementing image processing and manipulation algorithms to enable residue detection and characterization, logic and command operations execution and camera control. The computation means accumulates a database of on-line created wafer images and wafer residue defects, the computation means providing for inspection tool worthiness monitoring, wafer handling and transportation means.